Dieters often struggle to keep off the pounds they've lost, and a new
study involving mice offers a possible explanation. Dieting may change
how the brain responds to stress, so that the next time dieters feel
frazzled, they eat more, researchers say.

In the study, mice that previously had been put on a diet ate more high-fat foods than did mice with no history of dieting.

The altered eating behavior may be due, at least in part, to changes in genes that control the stress response and feeding habits, the researchers said.

The findings make sense from an evolutionary standpoint, said Tracy
Bale of the University of Pennsylvania and other study researchers. If
an animal has experienced famine, it would be advantageous for its brain
to change in ways that would protect the animal against another drastic
loss of calories, by promoting the consumption of high-fat foods.

But in today's environment, where high-fat foods abound, such a response encourages weight gain.

"This study highlights the difficult road that human dieters often
travel to attain and maintain their weight- loss goals," said Dr.
Jeffrey Zigman, an endocrinologist at the University of Texas
Southwestern Medical Center, who was not involved in the study. "It also
suggests that management of stress during dieting may be key to
achieving those goals."

Because the study was conducted in mice, research is needed to determine if the findings also apply to humans.

Researchers restricted the food intake of the mice in the study until
the mice had lost 10 percent to 15 percent of their weight, a reduction
typical of people on diets.

There also were chemical changes in the way the mice's bodies
regulated the release of another stress hormone, called
corticotropin-releasing factor, as well as melanin-concentrating hormone
and orexin, hormones thought to control eating behavior. These changes —
which are called epigenetic changes
and don't alter the genes' DNA sequence, but alter the way that
sequence is read by cells — remained even after the animals were allowed
to regain the weight.

Once the mice were back to their normal weight, they were subjected
to a series of stressful situations, including being placed in total
darkness, hearing new sounds at nighttime, and seeing a predator. A
group of control mice that had never been placed on a diet also were
exposed to these stressors.

All that stress led both groups of animals to binge when they were
later presented with high-fat food. However, more was consumed by the
mice that had dieted.

"These results suggest that dieting not only increases stress, making
successful dieting more difficult, but that it may actually 'reprogram'
how the brain responds to future stress and emotional drives for food,"
Bale said in a statement.

The study is published in the Dec. 1 issue of The Journal of Neuroscience.

Rachael Rettner

Rachael has been with Live Science since 2010. She has a masters degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a Bachelor of Science in molecular biology and a Master of Science in biology from the University of California, San Diego.